This invention relates to pumps driven by motors having fluid filled rotors, and more particularly to such pumps which use pressurized liquids within the rotor to maintain hydrodynamic bearing surfaces.
A low cost and highly reliable pumping system for use in critical applications, such as applications in which a thermal transfer fluid is directed through a tool that must be maintained at a particular temperature, is provided by a system described in U.S. patent application Ser. No. 09/906,624, entitled xe2x80x9cPump System Employing Liquid Filled Rotorxe2x80x9d, now U.S. Pat. No. 6,626,649, having Kenneth W. Cowans as inventor. In this system, the same thermal transfer fluid that is being pumped is also confined within a sealed rotor housing and used to serve as the fluid for supporting internal hydrodynamic bearings, even though the temperature of the thermal transfer fluid, as well as its viscosity, may be required by process conditions to vary within a substantial range. Typical thermal transfer fluids, such as a proprietary fluid sold under the trademark xe2x80x9cGaldenxe2x80x9d, or as one alternative a fifty/fifty mixture of glycol and water, neither solidify nor vaporize even though the hot and cold temperature limits vary widely. The design of the motor and pump system is such that thermal energy transfers between them are limited in all respects, specifically conduction through solids, conduction in the liquid, and convection. Thus the mean temperature within the enclosed rotor varies little, even though the temperature of the fluid circulated by the pump is at a much higher or lower level. 
It has been found, however, that under certain high load conditions, the localized temperature of the hydrodynamic films at the bearings within the rotor shell can substantially increase. In fact, the temperatures in these specific volumes can approach the vaporization point if the thermal transfer fluid being pumped is also in a higher temperature range. While the motor structure can be redesigned so that conductive fins dissipate some of this localized heat, this adds undesirably to cost, and sacrifices compactness. It is therefore desirable to preclude such localized fluid vaporization problems without imposing limitations on the operation of the pump/motor system, or employing special cooling structures for the bearings.
A pumping system employing a motor with a liquid filled rotor in accordance with the invention utilizes a regenerative turbine pump having an inlet angularly separated from the outlet for the pump, and an interior chamber in the pump housing that is in communication with an interior chamber within the fluid filled rotor of the motor. The passageways between the pump and the rotor communicate pressure without fluid transport, which would tend to equalize the temperature throughout the rotor chamber to the variable temperature at the pump.
In accordance with the invention, however, the volume within the pump chamber which communicates with the rotor interior is opened via conduits to the higher pressure at the pump outlet. This higher pressure in turn is established within the rotor interior. Such communication does not affect the pump operation, inasmuch as the substantial differential between inlet and outlet pressure is maintained. However, the increase in pressure within the rotor interior, which is dependent on the load on the pump, is highly significant. Under periods of high pump loading, when the local hydrodynamic bearing temperature tends to reach a peak, the pressure at the bearings is correspondingly increased. This consequently increases the fluid vaporization temperature level, automatically counteracting any boil off tendency at the bearing, while not otherwise affecting operation. Consequently, catastrophic or bearing fatigue effects which would be inimical to the desired goal of long life reliable operation of the pump, are avoided.
In a more specific example of a system in accordance with the invention, the regenerative turbine pump includes a turbine mounted within a pump housing that encompasses a protruding end of the motor shaft. The rotor housing incorporates bearing surfaces about the shaft on each axial side of the rotor. The pump inlet is parallel to the axis of rotation of the turbine, and the pump outlet is tangential relative to that the axis, the inlet and outlet being isolated from each other except for a circumferential channel about the turbine circumference. Blades on each side of the periphery of the turbine disk occupy most of the channel cross section. Fluid communication between the interior of the pump housing and the rotor shell interior is provided through an axial shaft conduit that extends between them. A small fluid interlink conduit in the pump housing between the pump outlet and the interior pump chamber hydraulically raises the interior rotor pressure with load via pathways extending between the high pressure turbine disk region and the rotor interior volume around the shaft. This provides pressure responsive temperature stabilization which avoids local heating in the bearing areas to levels which might approach the pressure adjusted vaporization temperature of the fluid.